Autonomous vehicles, such as vehicles that do not require a human driver, can be used to aid in the transport of passengers or items from one location to another. Such vehicles may operate in a fully autonomous mode where passengers may provide some initial input, such as a pickup or destination location, and the vehicle maneuvers itself to that location.
Robust operation of an autonomous vehicle or a vehicle operating in an autonomous driving mode requires proper response to unexpected circumstances, such as when a person such as a police officer, construction worker, firefighter, or other pedestrian is temporarily directing the flow of traffic. This can occur in construction zones, when a traffic signal light is out or broken, at the site of a traffic incident, or when there is a large event taking place. In such situations, vehicles may be required to stop, proceed, proceed only in a certain direction, turn around, etc. While this may be considered an inconvenience for a human driver, such human drivers are typically able recognize and to respond to these situations easily. While a human driver would not be able to recognize specific commands until very close to the person directing traffic, the human driver would understand conceptually that a person is directing traffic from a much farther distance. Today's computing devices may be able to recognize and respond to human gestures, but in order to do this most effectively, the vehicle's computing devices must first be able to determine that a person is temporarily directing traffic well before the person actually starts actually directing the vehicle.